Jay and Dirk are 18 miles apart and walking towards each other. Dirk is walking at 5mph and Jay at a more leisurely 4mph. Half way between them is a bee flying towards Jay at 6mph. When the bee reaches Jay it bounces off his nose and flies towards Dirk. When it reaches Dirk it bounces off his nose and flies towards Jay and so on back and forth. How far does the bee fly before Jay and Dirk collide and squash it?